Program SATORB

Program SATORB may be used to generate satellite orbits or to determine the orbits of satellites using (a) tabular satellite positions as pseudoobservations or (b) astrometric positions as real observations. More precisely the following problems may be solved:

1. Generation of satellite ephemerides using a wide variety of models.

2. Orbit determination using tabular positions or position differences as pseudo-observations. Two concrete problems may be addressed:

a) Orbit determination for GPS or GLONASS satellites using satellite positions in the SP3-format (or a special tabular format used in the Bernese GPS Software (see [58])) as pseudo-observations. No a priori information concerning the orbits other than the tabular positions is required to solve this task.

b) Orbit improvement for LEOs using satellite positions (and possibly position differences) as pseudo-observations. The positions and position differences stem from program LEOKIN (see section 7.2).

3. Orbit determination using astrometric positions following the use of program ORBDET (option "satellites"). Approximate osculating elements referring to the initial epoch are required in addition to the astrometric positions. The information stems from the program ORBDET.

Panel SATORB 1 in Figure 7.1 shows the primary menu of the program. The concrete program option is selected in the first input field. The three problem types are addressed in the next three paragraphs.

The following input files have to be defined in program SATORB:

• The file with constants shared by all programs of the package.

• The file with different geodetic datum definitions, which was already described in Chapter 8 (content see Figure 8.3).

Fig. 7.1. Primary menu panel of program SATORB

• A file containing the erp-parameters. The file may be retrieved from the address of the CODE analysis center http://www.aiub.unibe.ch/download/ BSWUSER/GEN/ under the file name BULLET_A.ERP. An example is provided in the subdirectory /GEN of the directory "CelestialMechanics" on the CD accompanying this book.

• A file containing the coefficients of the gravity field. Two examples (JGM3 and GEMT3) are contained in the subdirectory /GEN of the CD.

• A file with the coefficients of the UTCSR Ocean tide model (based on the Schwiderski model). The model is described and referenced in the IERS conventions [70].

• The JPL development ephemerides DE200 [111] are read from the binary file "de200.eph" in the same subdirectory. The file covers the time interval between 1981 and 2025. Other DE-files might be attached to the program to cover other time periods.

• The satellite information file is only needed when processing GPS positions. The file is described in [58].

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